Attitude Indicator
The attitude indicator (AI), also called the artificial horizon, is a gyroscopic flight instrument displaying the aircraft’s pitch and bank attitude relative to the earth’s horizon. It is the primary attitude reference during IMC and the centrepiece of the basic T instrument scan.
How It Works
A gyroscope maintains a fixed orientation in space (gyroscopic rigidity) while the aircraft rotates around it. The miniature aircraft symbol is fixed to the case; the horizon bar and bank angle indicator rotate with the gyro. The result: an intuitive pitch and bank display that replicates what you would see through the windscreen.
Errors and Limitations
- Precession: Gradual drift from true vertical; an erection mechanism corrects this in vacuum-driven instruments
- Tumbling (gimbal lock): Older mechanical AIs can topple in extreme attitudes; solid-state AHRS systems have no gimbal and do not tumble
- Acceleration error: Momentary false pitch indication during acceleration/deceleration
Vacuum vs. Electric
Traditional AIs are vacuum-powered. Electric backups or solid-state standby attitude indicators are essential for continued IMC flight if the vacuum system fails. Know your aircraft’s AI power source and the backup arrangement.
On the TC Written Exam
Know the six basic instruments, AI operating principles, failure modes, and partial-panel flying technique (flying with a failed AI). Cross-checking the turn coordinator and altimeter for attitude control without the AI is tested on the CPL IFR exam.
Related Terms
See also: Heading Indicator, Turn and Slip Indicator, IMC.